DESCRIPTION (provided by applicant ): The aims of the proposed study are to continue observing the natural history of Helicobacter pylori infection in children of low-income families in El Paso, Texas and Juarez, Mexico who have been followed previously from birth for 12-36 months as part of the Pasitos Cohort Study, which aims to identify factors that influence acquisition and persistence of infection in early childhood. Although it is known that H.pylori infection is associated with factors linked to low socioeconomic status, little evidence to date addresses the influence of environmental factors on the risk of acquiring the infection as opposed to the influence of these factors on the probability of having a persistent infection. The aim of our initial study was to observe the natural history of H.pylori infection during the first three years of life. Evidence suggests that ages 3-6 may be critical in determining whether infection persists throughout childhood into adulthood. Therefore, critical information will be gained from continuing to follow this cohort through six years of age. Specifically, we propose to: extend the original aims of the Pasitos Cohort Study to follow children through six years of age; estimate incidence rates of H.pylori infection in children living on both sides of the Rio Grande in El Paso, Texas and Juarez, Mexico from 3- 6 years of age; estimate rates of elimination of H.pylori infection in children from 3-6 years of age; and estimate the effect of socioeconomic indicators, hygiene, and diet on H.pylori incidence, recurrence, and persistence from 3-6 years of age. [unreadable] [unreadable]